1. Technical Field
This invention relates to the field of ultrasonic transducer systems generally and, in particular, to one in which a number of ultrasonic transducers are attached to a common support body.
2. Description of the Prior Art
Broad band ultrasonic transducers are employed in medical ultrasonic diagnostics and in the non-destructive testing of materials. Particularly in medical applications, where the losses in the coupling between tissue and a sonic transducer must be kept to a minimum, there is a need to improve the electro-mechanical and acoustic characteristics of these transducer systems.
An ultrasonic transducer is known where its ceramic transducer is coupled to a load medium, for example, tissue or water, through two .lambda./4 (quarter wave) matching layers. This transducer system consists of a backing of epoxy resin having an acoustic impedance of 3.times.10.sup.6 Pas/m, a ceramic transducer, a first .lambda./4 matching layer of glass with an acoustic impedance of 10.times.10.sup.6 Pas/m and a second .lambda./4 matching layer of polyacrylate or of epoxy resin with an acoustic impedance of 3.times.10.sup.6 Pas/m. The ceramic transducer is attached to a backing. The attachment of the glass plate as the first .lambda./4 matching layer is accomplished with an adhesive cement of very low viscosity, so that the thickness of the adhesive cement is in the order of 2 um. The epoxy resin as the second .lambda./4 matching layer is poured directly over the first .lambda./4 matching layer. Through these double .lambda./4 matching layers, one only obtains an improvement in the bandwidth of the ceramic radiating layer. The bandwidth of this ultrasonic transducer is about 60 to 70% of the mid-frequency. (Experimental Investigation of Ultrasonic Transducers--Biomedical Technology--volume 27, issue 7 to 8, 1982, pages 182 to 185).
Another ultrasonic transducer has been proposed having a radiating layer made of a material with a comparatively high dielectric constant and high acoustic impedance and which employs two .lambda./4 matching layers. The first .lambda./4 matching layer which faces the radiating layer has an acoustic impedance of about 14.times.10.sup.6 Pas/m and is made, for example, from porcelain or a glass-like material (macor), preferably of quartz glass. The second 80 /4 matching layer which is facing the load has an acoustic impedance of about 4.times.10.sup.6 Pas/m and is made, for example, from polyvinylchloride PVC or, more particularly, from polyvinylidine flouride PVDF, and can also be employed as a receiving layer. In addition, the first .lambda./4 matching layer is used as a backing for the receiving layer. Through this configuration an ultrasonic transducer is obtained having a radiating layer that may be coupled to a load with minimum reflection and broad bandwidth and which has a receiving layer of unusual sensitivity and bandwidth. (German patent application No. P33 09 236.2).